The field of art to which this invention pertains is radiation curable acrylated polyurethanes.
Due to environmental concern and the high cost of solvents, commercial interest in radiation curable compositions is constantly increasing. Federal, state and local government legislation which restricts the amount of solvents and other pollutants that can be vented to the atmosphere is one reason for this increased interest. Other reasons are the concerns expressed by unions and individuals over the possible toxic effects of prolonged exposure to volatile organic materials and also the high cost of petroleum derived solvents. Generally, radiation curable systems are essentially 100% reactive systems, i.e., substantially all of the components react to produce the final product. Such systems can be cured by exposure to high energy ionizing radiation or to actinic radiation in the presence of photoinitiators.
Among the various radiation curable compositions disclosed in the prior art are polyurethane oligomers which have terminal acrylyl or methacrylyl groups. These are generally produced by the reaction of one or more organic polyisocyanates with one or more organic polyols wherein at least a portion of the polyisocyanate or polyol reactant has, in addition to its isocyanate or hydroxyl functionality, acrylyl or methacrylyl groups. Such radiation curable polyurethane oligomers can be made by reacting a stoichiometric excess of a polyisocyanate with a polyol and then reacting the remaining isocyanate groups with a hydroxyalkyl acrylate or methacrylate. U.S. Pat. No. 3,700,643 discloses radiation curable oligomers made by reacting a polycaprolactone diol with an organic diisocyanate in a mole ratio of one to two followed by reaction with hydroxyethyl acrylate. In U.S. Pat. No. 3,782,961 a hydroxy compound having at least 5 ether linkages and a terminal acrylate or methacrylate group is reacted with a polyisocyanate.
U.S. Pat. No. 4,133,723 discloses radiation curable compositions made by reacting a polyalkylene polyol having from 2 to 6 hydroxyl groups with a molar excess of a diisocyanate followed by reaction with a hydroxyalkyl acrylate or methacrylate.
U.S. Pat. Nos. 4,057,431 and 4,139,436 describe photopolymerizable compositions made by reacting a polyether polyol having 2 or 3 hydroxyl groups with an organic polyisocyanate and a hydroxyalkyl methacrylate. The reaction can be conducted in a diluent such as a polyethylene polyol acrylate or methacrylate.
Low viscosity radiation curable compositions are described in U.S. Pat. No. 4,131,602. Such compositions are made by reacting an organic diisocyanate with a combination of organic tri/tetraol and organic diol followed by reacting a hydroxyalkyl acrylate. The combination of polyols is either a polyester tri/tetraol-polyether diol or a polyether tri/tetraol-polyester diol.
Additional patents which disclose radiation curable polyurethane oligomers are U.S. Pat. Nos. 3,929,929; 4,089,763; 4,174,307; 4,309,526 and 4,312,798.
Constant efforts are being made to improve the properties of radiation curable compositions. In the radiation curable coatings area, there is a need for compositions which have enhanced cure response, and, after being cured, improved abrasion resistance and improved tensile strength.